The use of the lead salts, such as lead sulfide (PbS) and lead selenide (PbSe), as photoconductive materials for infrared detector arrays is well known in the art. These detector materials have been used in various array geometries for many years and conventionally they are deposited initially as a polycrystalline film on a suitable insulating substrate. State of the art processes use conventional photoresist masking and etching techniques to form an array of discrete lead sulfide or lead selenide islands on the surface of the substrate.
In order to improve the resolution of imaging devices using these arrays, it frequently becomes necessary to increase the number of discrete photoconductive elements per array, and this in turn requires a corresponding increase in the number of electrical contacts made on a particular array surface. Additionally, it has been established empirically that the best performance of these arrays is obtained when electrical contacts are made exclusively to the surfaces of the photoconductive detector elements of the array exposed to incoming radiation, i.e. the top surfaces.